This has been an impossibly difficult week for Jim Pitzen. His wife, 43-year-old Amy Fry-Pitzen, was found dead in a Rockford, Illinois hotel room on Saturday, an apparent suicide. Their only child -- 6-year-old Timothy -- was last seen with his mother a week ago. He is still missing.

"He's out there somewhere and I know he's okay. I just want him to come home to his family," said Jim Pitzen, who is determined to hold on to hope.

Police in the Pitzens' hometown of Aurora, Illinois say Timothy's mother left a suicide note.

"It said she left the boy with people would care for him and love him," said Lt. Pete Inda, "but she didn't name any names."

Police have handed out hundreds of flyers, and mounted massive searches in parts of Wisconsin, Illinois and Iowa. Their efforts, using helicopters, search dogs and dozens of officers, have turned up precious little. On Thursday, about 70 investigators combed through state parks, highway rest areas and overpasses near Dixon, Illinois, the last place relatives heard from Fry-Pitzen on her cell phone.

"We searched 25 places yesterday, but nothing was found that would indicate where Timothy is," said Lt. Inda, who is looking at a number of theories, including one he doesn't want to think about -- that Timothy is no longer alive. "Because he's not been located, every day that goes by it gets worse and worse to think of that possibility."

Mother and son were last seen a week ago. On May 11, investigators say Fry-Pitzen signed her son out of his kindergarten class, and took him to the Brookfield Zoo. Later, they checked into the Key Lime Cove Resort, a water park in Gurnee, Illinois.

Jim Pitzen said he had no idea his wife and son were missing until he tried to pick Timothy up from Kindergarten last Friday, "I went to pick him up from school, and he was gone," said Jim Pitzen, who is still trying to understand his wife's actions. "What was she thinking? What was going through her mind?"

Police say Pitzen made repeated calls to his wife, but she never answered her cellphone.

Credit card receipts indicate mother and son traveled to Racine, Wisconsin the next day, and checked into the Kalahari Resort, another water park in the Wisconsin Dells, that night. Surveillance tape from the resort shows Timothy wearing blue shorts and a brown T-shirt with white socks.

Relatives last heard from Timothy last weekend by cellphone. "She called and seemed fine," said Lt. Inda, "Timothy made a comment to a relative that he was hungry, so we assume they stopped for something to eat."

That was the last anyone heard from Timothy or his mother. On May 13, Fry-Pitzen was seen alone in a grocery store in Rockford, Illinois -- near the hotel where her body was later discovered. Timothy's car booster seat and his Spider-Man backpack were missing from his mother's Ford Expedition, found in the hotel parking lot.

Relatives hope that means Fry-Pitzen may have left her son somewhere safe, but that is of little comfort to Timothy's father.

"It pains me to think he may be out there with someone else while all of this is going on. "

Timothy's kindergarten classmates have tied yellow ribbons around the trees on school property, a gesture of hope for his safe return.

Timothy is described as 4 feet 2 inches, about 70 pounds, with brown hair and brown eyes. His father is imploring anyone with information to call police.

"I'm hoping someone will say, 'I've seen this boy today' and we'll get him back," said Jim Pitzen, "Today's really bad, and tomorrow will be worse."